JLG 600SC_660SJC Service Manual - Manual (Page 134)

SECTION 4 - BOOM & PLATFORM
4-32 – JLG Lift – 3121607
Troubleshooting Table 4-1. Troubleshooting
Problem Cause Solution
1. Shaft rotates slowly or not at all a. Insufficient torque output
b. Low rate of fluid flow
c. Control or counterbalance valve has internal leak
d. Piston and/or shaft seal leak
e. Corrosion build-up on the thrust surfaces
f. Swollen seals and composite bearings caused by incom-
patible hydraulic fluid
a. Verify correct operating pressure. Do not exceed OEM’s
pressure specifications. Load may be above maximum
capacity of the actuator.
b. Inspect ports for obstructions and hydraulic lines for
restrictions and leaks.
c. Disconnect hydraulic lines and bypass valve. Leave valve
ports open and operate actuator through housing ports (do
not exceed OEM’s operating pressure). Valve must be
replaced if a steady flow of fluid is seen coming from valve
ports.
d. Remove plug and housing’s valve ports. Operate actuator
through housing ports. Conduct internal leakage test.
e. Rebuild actuator. Remove all rust then polish. Replace-
ment parts may be needed.
f. Rebuild actuator. Use fluid compatible with all seals and
bearings.
2. Operation is erratic or not responsive a. Air in actuator a. Purge air from actuator. See bleeding procedures.
3. Shaft will not fully rotate a. Twisted or chipped gear teeth
b. Port fittings are obstructing the piston
a. Check for gear binding. Actuator may not be able to be
rebuilt and may need to be replaced. Damage could be a
result of overload or shock.
b. Check thread length of port fittings. Fittings should dur-
ing stroke not reach inside housing bore.
4. Selected position cannot be maintained a. Control or counterbalance valve has internal leak
b. Piston and/or shaft seal leak
c. Air in actuator
a. Disconnect hydraulic lines and bypass valve. Leave valve
ports open and operate actuator through housing ports (do
not exceed OEM’s operating pressure). Valve must be
replaced if a steady flow of fluid is seen coming from valve
ports.
b. Remove plug and housing’s valve ports. Operate actuator
through housing ports. Conduct internal leakage test.
c. Purge air from actuator. See bleeding procedures